Power supply technology belongs to a category of power electronic technology, and is an edge cross subject integrating many disciplines, such as power conversion, modern electronics and automatic control, and has been widely applied in various fields nowadays, such as industry, energy sources, traffic, IT, aeronautics, national defense, education, and culture. In fact, development of the power supply technology is concentrated on diligent studies conducted for improving an efficiency and a performance, reducing in size and weight, being safe and reliable, eliminating power public nuisance, and reducing electromagnetic interference and traces of electric noise, a switching power supply is a crucial part in the whole power supply technology, where, a compensation network of a Pulse Width Modulation (PWM) power supply regulator is an important research subject of the switching power supply.
Generally, a switching power supply circuit is composed of three basic modules, as shown in FIG. 1, which include: a power switching regulator 11, a low pass filter network 12 and a compensation network 13. The power switching regulator 11 is configured to generate a square wave signal, to control an ON/OFF state of a power tube; the low pass filter network 12, i.e., an LC network, is configured to filter an output voltage and current, to generate an LC double pole; the compensation network 13 is composed of a voltage sampling circuit, an error amplifier and a compensation circuit element.
An error amplifier is often used in design of a switching power supply circuit, if a low-frequency gain desired by the switching power supply circuit is very high, there is a need to compensate the error amplifier in the compensation network, so as to guarantee that the switching power supply circuit has a great bandwidth and a good phase margin. A high low-frequency gain is required by the switching power supply circuit in a voltage mode, but a power-stage transfer function has a low low-frequency gain, and there is a pair of LC conjugated poles, therefore there is a need to add an error amplifier to obtain a high low-frequency gain and meanwhile compensate the error amplifier to eliminate influence of the conjugated poles, so as to make the switching power supply circuit have a high phase margin at the same time of obtaining a great bandwidth.
As shown in FIG. 2, a conventional compensation network adopts a solution that two ends of an error amplifier AMPO are bridged with resistance capacitance networks, and the compensation network composed of resistors R6, R7, R8 and capacitors C5, C6, C7 just can compensate three poles and two zeros in the original switching power supply circuit. The switching power supply circuit obtained in such way can obtain a high bandwidth and phase margin at a low frequency, have a small gain at a switching frequency, and thus have a good suppression effect on switching noises. However, when a switching frequency required by the switching power supply circuit is high, stability of the switching power supply circuit cannot be guaranteed any more due to a pole effect of the error amplifier itself. Additionally, a pole would also be introduced when an input end of the error amplifier needs to be connected with a voltage dividing resistor, which has a great effect on compensation.